This invention relates to a needle-bar disconnecting device on a sewing machine for connecting and disconnecting a needle bar to and from a needle-bar connecting stud moving vertically synchronously with the rotation of an arm shaft.
When fabric is embroidered, basted, or sewn, the movement of the needle bar is stopped temporarily and fabric is fed without being sewn. For that purpose, a device for stopping the movement of the needle bar is used. A device for stopping the rotation of an arm shaft is known. A device for stopping a counterbalancing crank with a clutch provided between the arm shaft and the counterbalancing crank is also known. However, the inertia of stopped components of these known devices is so large that at the time of restart a large load is applied to the clutch and other components. To solve this problem, Japan Published Examined Utility Model Application No. S61-25752 and Japan Published Unexamined Patent Application No. S59-194792 are proposed. In these related-art references, a clutch is provided between a needle-bar connecting stud and a needle bar, and only the needle bar is stopped. Another related-art device proposed in Japan Published Unexamined Utility Model Application No. S62-139472 is applied to a zigzag sewing machine. In this device a needle bar is rotated in a width larger than that of a zigzag form sewn. The rotation of the needle bar actuates a clutch for disconnecting the needle bar from a needle bar connecting stud.
Further, threading the needle of a sewing machine presents related problems. To facilitate threading, various threading devices are proposed. For example, in Japan Published Unexamined Patent Application No. H1-113092, a spring exerts an upward force on an actuating rod. The actuating rod is lowered by an air cylinder. A threading rod interlocks with the actuating rod, lowers, and rotates. A threading hook thus goes through an eye in a needle and catches a thread. Subsequently, when the threading hook is drawn from the eye, thread is also drawn and the needle is threaded.
In the related art, some sewing machines are provided with both the needle-bar disconnecting device and the threading device. However, when these related-art devices are both used in a sewing machine, a drive source for actuating the clutch and disconnecting the needle bar must be mounted separately from the drive source required for threading. Therefore, the devices occupy excessive space in the sewing machine. At the same time, since the devices must be controlled separately, a complicated control device is required.
The needle bar is disconnected from the needle-bar connecting stud through a pulse motor, and the pulse motor can also be used for the rotating of the needle bar. However, every time the needle bar disengages from the needle-bar connecting stud, the needle bar laterally moves. The resulting problem is that the relative position among a thread guide, an eye in a needle, and stitches causes variances in thread amount and tension. At the same time, the lateral movement of the needle bar may mar the fabric.